"As a Japanese citizen, and as a local lawmaker, I went onto the island to show clearly that this is Japan's territory," Eiji Kousaka, a parliament representative from Tokyo, told the Reuters news agency after landing on the island.

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The island is part of an uninhabited chain in the East China Sea claimed by both countries. China calls them Diaoyu and Japan calls them Senkaku, and ownership of the islands would allow for exclusive oil, mineral, and fishing rights in surrounding waters.

After Japan arrested the Chinese group Wednesday, there were anti-Japan demonstrations in Shanghai, Hong Kong, and Beijing.

China warned Japan not to allow Sunday's landing, urging it not to "undermine China's territorial sovereignty," according to China's state-run Xinhua news agency.

The islands have been the center of dispute for decades.

Japanese nationalists traveled to the islands in 1990 and 1996. In 2010, tensions rose to a boiling point when a Chinese fishing trawler rammed into a Japan Coast Guard vessel on patrol in the islands' waters. Japan detained the crew members but later released them under Chinese diplomatic and trade pressure.

The dispute boils down to where lines can be drawn in the ocean for commercial use. International law allows for a nation to claim exclusive economic rights to fish, oil and mineral reserves up to 200 nautical miles from the shore.

One question hanging over territorial claims is whether the disputed islands are islands at all, according to maritime law. If they're not islands, then territorial claims don't apply.

Both sides say they have a history of economic use of the islands. China points to a 1893 decree by Dowager Empress Cixi, giving the island to a Chinese medicine-maker for use in cultivating herbs. Japan points to 19th-century use on the island to collect seabird feathers and guano.

Tokyo Gov. Shintaro Ishihara says a Japanese family claims to own four of the five disputed islands, and that it has documents showing the islands' Japanese ownership dating to 1890.

The Wednesday incident coincided with the 67th anniversary of Japan's official World War II surrender. On the same day, two Japanese Cabinet ministers visited the controversial Yasukuni shrine in Tokyo, which honors Japan's war dead as well as war criminals.

China and South Korea, given their respective wartime occupation and colonization by Japan, have condemned such visits.

A commentary published by the Japan Times on Friday cited diplomatic experts in Japan as saying both nations would benefit from resolving the dispute quickly, with China facing a leadership change later in the year and Japan facing separate territorial fights with Seoul and Moscow.

Adding to the regional tensions before the anniversary was South Korean President Lee Myung-bak's visit Tuesday to what the country calls Dokdo, a small group of islands in the Sea of Japan that Japan claims as Takeshima.

The move prompted Japan to recall its ambassador to Seoul and warn South Korea that it will take the issue to the International Court of Justice -- a proposal rejected by Seoul. Japan's finance minister has also said he will cancel a trip to South Korea because of the dispute.

Japan has long claimed the islets as its territory, but Seoul said all Korean territory was returned after the country won independence from colonial rule by Japan in 1945.